This invention relates to a magnet position and orientation measurement system. In the prior art, numerous examples are found of systems which use Hall-effect devices for various purposes and which with or without the use of Hall-effect devices attempt to accurately locate an object within a given space. Unfortunately, most of these systems are complicated and extremely expensive and usually require control of both the source and sensor from a microprocessor. Further, no prior art known to applicant discloses an invention which determines both the position and orientation of an object within a given space utilizing a sensor unconnected to the microprocessor and capable of measurement in five degrees of freedom. The following prior art is known to applicant:
U.S. Pat. No. 3,133,244 discloses a three dimensional magnetic detector which includes a cube boss and orthogonal poles extending therefrom. This device is distinct from the present invention for many reasons including the fact that the sensing elements thereof are coils rather than the Hall-effect devices in applicant's invention and further because there is no disclosure therein of the measurement of position and orientation of an object.
U.S. Pat. No. 3,189,762 discloses a three dimensional Hall-effect sensor including orthogonal legs and electrodes. While this device is similar to the three-axis antennas described hereinafter, the disclosure in this patent is merely similar to a subcombination of applicants invention and does not suggest or teach the measurement of position or orientation of an object in a space.
U.S. Pat. No. 3,373,273 discloses in FIG. 2 thereof a Hall-effect body including electrodes on each of its six surfaces. Three coils are provided as magnet means for producing three coordinate magnet components to which the Hall-effect body is subjected. An electrical vector product is generated by the system, however, no position or orientation measurements are made.
U.S. Pat. No. 3,564,402 discloses in FIG. 4 thereof a Hall-effect apparatus for sensing three orthogonal components of a field vector. The field vector is randomly oriented and no position or orientation measurements are made. Further, while the sensing device disclosed therein may be utilized in the system of the present invention, it only comprises a mere subcombination thereof.
U.S. Pat. No. 4,109,199 discloses a three axis magnetometer best seen in FIG. 5 thereof to comprise three mutually orthogonal coils. The main difference between this device and the devices utilized in the system of the present invention comprises the fact that no Hall-effect devices are used but, rather, coils are used. Further, no position or orientation measurements are made.
U.S. Pat. No. 3,591,788 discloses a system which obtains the ordinates of one of two objects, one of which is a ferromagnetic recording medium and the other of which is an electromagnetic pickup head. The electromagnetic pickup head includes a Hall element and the recording medium includes means to detect a second signal on a parallel track. In this device, no position or orientation measurements are made, no three-dimensional sensing device is used and no permanent magnet-type target object is used.
U.S. Pat. No. 3,661,089 discloses an automated vehicle which includes a code reader having Hall-effect devices included therewith which sense the orientation of code magnets to thereby perform tasks based upon signals indicative of such orientation. This system is vastly different from the system disclosed herein and with regard to the sensing of orientation, only two opposed orientations of the code magnets may be determined, and orientations thereof between these two positions are not determined.
U S. Pat. No. 3,644,825 discloses a pair of orthogonally oriented field sensors. The signals received from these sensors are combined vectorally so that the direction of movement and/or relative position of an object may be determined. As illustrated in FIG. 2, the object may include a permanent magnet which creates a magnetic field. There are many differences between this patented invention and the invention disclosed herein, including: (1) only the x,y coordinates of the position of the object are determined; (2) the determination of the position of the object is only made in zones; (3) no orientation measurement of the magnet is made; (4) no Hall-effect devices are used in the system; (5) the system does not use three dimensional magnetic field sensing devices; (6) there is no position finding algorithm which calculates the position as is used in the present invention.
U.S. Pat. No. 3,842,419 discloses a system best shown in FIG. 1 to include a center antenna and two side antennas. An emitter emits an electromagnetic wave and the position of the emitter is calculated by computing the phase difference of signals emitted from the emitter with each antenna comprises a triad. This system is distinctly different from the system disclosed in this patent application especially in that applicant's system produces a magnetic field from a permanent magnet at zero frequency and does not rely upon phase differences to sense position. Further, the patented invention provides no position measurement but rather provides a direction measurement and no orientation measurement in three degrees of freedom is made.
U.S. Pat. No. 4,054,881 discloses three mutually orthogonally radiating antennas each of which transmits electromagnetic radiation to three mutually orthogonal receiving antennas. The receiving antennas measure the radiated signals and produce nine parameters which enable calculation of the position and orientation of the receiving antennas with respect to the transmitting antennas. There are several differences from this patented invention and the invention disclosed herein, including: (1) the present invention utilizes a permanent magnet which generates a magnetic field at zero frequency whereas the patented invention utilizes a transmitted magnetic field at a frequency of 10 kHz; (2) the target in the patented system utilizes amplifiers, filters, a processor and a power supply to generate the transmitted signal whereas the target in the present invention is merely a passive permanent magnet which generates a magnetic field at zero frequency; (3) the patented system utilizes a three-axis transmitter and a three-axis receiver whereas the present invention utilizes a one axis target and two or three three-axis magnetic field sensing devices which are of the Hall-effect type; (4) the algorithms utilized for position and orientation determination are vastly different from one another.
U.S. Pat. No. 4,163,326 discloses the use of two Hall-effect semiconductor devices disposed at right angles to one another. A magnetic field is directed at a particular angle with respect to the Hall-effect devices and this angle may be determined through calculations involving the Hall voltages. This device comprises a compass which is utilized only to measure the direction of earth's magnetic field. This is vastly different from the present invention which compensates for the earth's magnetic field before operations to calculate the position of permanent magnet within a prescribed space begin. Further, the patented invention discloses no determination of the position or orientation of a movable object.
U.S. Pat. No. 4,197,855 discloses a system wherein a permanent magnet is planted, for example, in the human jaw and three orthogonal sensors are provided which are sensitive to the magnetic flux created by the permanent magnet and the system enables calculation of the location and orientation of the magnet. The orthogonal sensors comprise Hall-effect devices. Several differences between this patented system and the present invention are evident as follows: (1) the "permanent magnet" in reality comprises two permanent magnets. In the present invention, a simple permanent magnet rod is utilized; (2) the sensing elements in the patented invention are arrays of Hall-effect devices whereas the present invention utilizes only two or three three-axis magnetic field sensing devices separated by significantly greater distances than the arrays in the patented invention; (3) the patented system requires that the sensing arrays be placed close to the permanent magnet whereas in the present invention, much greater separation is possible; (4) the patented invention requires the use of an extremely large number of Hall-effect devices whereas the system of the present invention utilizes only six or nine Hall-effect devices.
U.S. Pat. No. 4,232,451 discloses a detector which detects the orientation of a rotating magnet. The detector includes a plurality of Hall-elements which detect flux changes representative of orientation of the magnet with respect to the detector. This patent is vastly different from the invention disclosed in this patent application in that the patented invention does not measure the position of the object, only one degree of freedom is measured whereas in the present invention three degrees of freedom are measured and further no three dimensional magnetic field sensing devices are utilized.
U.S. Pat. No. 4,328,548 discloses an invention which detects the position of a source of electromagnetic radiation. Three orthogonal components detect and measure components of the received radiation to enable calculation of the position of the source of the radiation. This system is vastly different from the system disclosed herein for the following reasons (1) the patented system utilizes coils as transmitters and coils as receivers with the respective coils being placed orthogonal to one another; (2) the system requires frequency synthesizers in both the transmitter and the receiver in a signal selection scheme; (3) the system utilizes a time varying electromagnetic field; (4) the transmitter in the patented system which is in essence the target utilizes amplifiers, filters, synthesizers and a power supply whereas the target in the present invention is merely a simple permanent magnet.
The following U.S. Patents are also known to applicants and are believed to be of only general interest: U.S. Pat. Nos. 2,597,125, 2,715,995, 3,002,691, 3,551,649, 3,797,015, 3,851,395, 3,863,257, 4,086,533, 4,229,696, 4,327,498, 4,295,118, and 4,336,596.
The following prior art publications are also known to applicant and are believed to be of only general interest:
"Magnetic Position and Orientation Tracking System" by Raab, et al., IEEE Transactions on Aerospace and Electronic Systems, Volume 15, Number 5, Sept. 1979, is believed to be related to U.S. Pat. No. 4,054,881 to Raab discussed hereinabove and the present invention is believed distinct from this publication for the same reasons discussed regarding U.S. Pat. No. 4,054,881.
Publication "Electromagnetic Retransmission System for Locating Trapped Mine Workers", final report on contract No. H0188071, Polhemus Navigation Systems, Inc. Essex Junction, Vt., Feb., 1980, chapter 1, discloses the use of "Three three-axis sources", however since the systems disclosed all use electromagnetic transmission rather than Hall-effect, this publication is believed to be only generally related to the present invention.